The present invention concerns a rope of synthetic fiber with several ropes running parallel and spaced apart with a common rope sheathing, e.g., for use in an elevator installation.
Running ropes are in the conveying technology, in particular in the case of elevators, in the crane construction and in the mining industry, an important highly strained machine element. Particularly, the strain in driven ropes is multi-layered, as they are used, for example, with cranes and elevators.
In the case of conventional elevator installations, the car sling and a counterweight are connected to each other through several steel stranded ropes. In order to lift and lower the car and the counterweight, the ropes run over a driving disk, pulley or sheave, which is driven by a drive motor. The driving torque generated by the drive motor is, under frictional engagement, impressed on the rope section, which respectively contacts the driving sheave at a belt wrap: At the same time, the ropes experience tensile stress, bending stress, compressive strain and torsional stress. The relative motions, originating from the inflection upon the pulley, give rise to friction within the rope structure, which can, depending upon the lubricant concentration, negatively affect the rope wear. Depending upon rope construction, bending radius, groove profile and rope safety factor, the emerging primary and secondary stresses have a negative influence on the condition of the rope.
Apart from the strength requirements and in addition for energy reasons, in the case of cranes and elevators the demand exists for small rope masses, if possible. High-strength ropes of synthetic fiber, as for example made of aromatic polyamide, in particular aramides, with high-grade oriented molecular chains, fulfil these requirements better than steel ropes, however they have a lower transverse strength.
Consequently, in order to expose the aramide fibers when running over the driving disk to the lowest possible transverse strength, for example in the European patent document EP 0 672 781 A1 is suggested a parallel turned aramide fiber stranded rope, which is suitable as driving rope. The well-known aramide rope, shown in the European patent document EP 0 672 781 A1, offers very satisfying values regarding life span, higher abrasion resistance and fatigue strength under reversed bending stresses; however, in case of unfavorable circumstances, the possibility exists that in the case of parallel stranded aramide ropes, partial rope untwisting features appear, which disturb the original rope structure lasting in their balance. These torsional effects and the changes of the rope structure can be avoided, for example, with a rope of synthetic fiber in accordance with the European patent application EP 1 061 172 A2. For this purpose, the rope of synthetic fiber comprises two parallel running ropes, which are connected to each other through a rope sheathing. The rope of synthetic fiber, in accordance with EP 1 061 172 A2, attains a longitudinal strength essentially through the characteristics of both the parallel running ropes. On the other hand, the rope sheathing prevents the torsional effects and changes of the rope structure. In addition, the rope sheathing serves as isolation (protective effect) and it exhibits a high coefficient of friction.
A weak point can be, depending upon the planned use and range of application, the fixed link of such a rope of synthetic fiber in accordance with EP 1 061 172 A2.